A valve assembly regulates flow of a fluid or movement of a device by controlling the flow of a separate working fluid responsive to an electrical control signal.
Emission control systems for internal combustion engines recirculate a portion of the exhaust gases emitted from the engines back through the combustion process to lower harmful emissions. Exhaust gas recirculating valves (EGRV) connected to exhaust manifolds divert metered amounts of the exhaust gas to intake manifolds for re-burn by the engine. The exhaust gases are mixed with fresh air/fuel mixtures resulting in a lowering of combustion temperature and a reduction in the formation of harmful compounds such as nitrous oxide.
The invention features a two-stage proportional flow control valve assembly that is particularly useful for regulating exhaust flow rates in exhaust gas re-circulating systems of internal combustion engines. Electrical control signals from an engine control module (ECM) regulate the exhaust flow rates through an exhaust valve utilizing engine oil pressure to produce a hydraulic actuating force. Since the electrical control signals are not required to provide the force for opening or closing the exhaust valve, my new two-stage proportional flow control valve assembly conserves electrical power for other functions.
An exemplary two-stage proportional flow control valve assembly adapted for use as an exhaust gas recirculating valve incorporates an exhaust valve that regulates exhaust flow rates recirculated to an engine and a directional valve that utilizes engine oil pressure for regulating opening and closing of the exhaust valve proportional to control signals from an engine control module (ECM). Moveable components of the exhaust valve are preferably pressure balanced with respect to the flow of exhaust gas through the exhaust valve to optimize positional accuracy. A fluid-powered actuator movable under the influence of engine oil pressure provides the necessary force for opening and closing the exhaust valve. The directional valve controls flow of the pressurized engine oil to the fluid-powered actuator to adjust the position of the exhaust valve proportional to the control signal.
The movable portion of the exhaust valve is preferably a pressure-balanced dual poppet head body with each of two poppet heads having an approximately equal opposing area exposed to exhaust gas pressures. The dual poppet heads translate along a central axis for opening and closing exhaust passages encircled by mating poppet seats. The fluid-powered actuator is preferably a double-acting cylinder having a piston mechanically coupled to the dual poppet head body for effecting common movement along the central axis. The directional valve is preferably a four-way servovalve in the form of a spool valve that regulates flows of pressurized engine oil to opposite faces of the piston. The spool valve includes a spool also movable along the central axis between (a) an initial position that charges a proximal face of the piston with the pressurized engine oil for moving the piston in a direction that closes the exhaust valve and (b) an actuated position that charges a distal face of the piston with the pressurized engine oil for moving the piston in a direction that opens the exhaust valve.
An electrical actuator preferably in the form of a proportional solenoid under control of the electronic control module (ECM) converts the control signals of varying current into proportional forces imparted by an armature against the spool along the central axis. A feedback mechanism, preferably in the form of a compression spring, also located along the central axis, applies a separating force between the spool and the piston proportional to its displacement. An adjustable null compression spring or other biasing mechanism biases the solenoid armature against the spool. Thus, the spool and the armature are preferably biased together from opposite directions by two springsxe2x80x94the null spring acting on the spool in the same direction as the solenoid armature and the feedback spring acting on the spool in the opposite direction.
In the absence of an actuating force from the solenoid, the feedback spring, which is the stronger of the two springs, biases the spool against an armature stop, which corresponds to the initial spool position at which the proximal face of the piston is pressurized for closing the exhaust valve. Compression of the null spring can be adjusted to establish a proper take-off current to the solenoid at which the sum of the forces imparted by the null spring and the solenoid are sufficient to move the spool against the feedback spring. Additional current moves the spool further against the feedback spring to the actuated position at which the distal face of the piston is pressurized for opening the exhaust valve.
Upon reaching the actuated position, further movement of the spool is limited by contact between the solenoid armature and the armature stop. The initial and actuated positions can be adjusted to set maximum flow rates through the spool valve in either direction. Movement of the spool to the actuated position compresses the feedback spring up to the limit set by the armature stop. Movement of the piston in response to the charging of its distal face further compresses the compression spring until a counteracting force exerted by the piston through the compression spring momentarily exceeds the sum of the forces exerted on the spool by the null spring and solenoid and returns the spool to a so-called neutral position (i.e., a position between the actuated and the initial positions) at which further flow to the piston is stopped.
Actuating forces exerted by the solenoid above the take-off current temporarily move the spool beyond the neutral position until the counteracting force of the piston returns the spool to the neutral position. Although the spool returns to the same neutral position throughout the intended range of solenoid actuating forces above the take-off current, the piston""s position (and with it the position of the dual poppet head body of the exhaust-valve) varies directly with the compression of the feedback spring. Any change in the actuating force produces a corresponding change in the compression of the feedback spring, which exerts a force equal and opposite to the sum of the forces exerted on the spool by the null spring and the solenoid. The force exerted by the null spring remains the same at the neutral position, so the change in the force exerted by the feedback spring matches the change in the force exerted by the solenoid.
The feedback spring is the sole mechanical connection between the piston and the spool. The amount that the feedback spring is compressed is controlled by the amount of current that is applied to the solenoid. Movement of the spool to the actuated position starts the compression of the feedback spring, and the engine-oil powered displacement of the piston completes the required compression of the feedback spring while restoring the spool to the neutral position. The amount of compression of the feedback spring determines the spacing of the piston from the spool in the neutral position. Changes in the position of the piston are accompanied by corresponding changes in the position of the dual poppet head body of the exhaust valve.
The control signal (i.e., current) to the solenoid provides a proportional control that modulates both opening and closing of the exhaust valve, while the force for actually operating the exhaust valve is derived from engine oil pressure. Neither changes in the engine oil pressure nor changes in the external pressure applied to the dual poppet head body unduly affect the exhaust valve position. The spool valve maintains the position of the piston independently of overall oil pressure, which can affect flow rates but not ultimate positions of the valve components. The neutral position blocks flows to or from either side of the piston to maintain the exhaust valve in a desired position. Balancing the dual poppet head body to exhaust gas pressures also limits the influence of the exhaust gas pressures or flow rates on the valve position. This independence of the new two-stage proportional control valve from changes in the exhaust and engine oil pressures, together with the linear and proportional modulation of flow rates through the exhaust valve with respect to the electrical control signal, makes this new valve particularly accurate, reliable, and robust.
The new valve is expected to contribute to reducing harmful engine emissions while operating more efficiently by utilizing engine oil pressure to move the exhaust valve. The valve is also expected to have a variety of other uses in situations where proportional movement of a valve or other device is modulated by low-power control signals regulating the flow of working fluid in an intermediate actuator.